Serious question, have you used a phone with an in-screen fingerprint sensor yet? The OnePlus 6T is not good. You need to hit the spot perfectly every time. Not only that, it can be wildly wonky at times. It is not nearly as quick of a process as traditional fingerprint sensors because you can't feel it when you aren't looking at or holding the phone. Yes I know Samsung is using an ultra sonic sensor and not optical. But you still need to perfectly place your finger on it.
I owned and sold the 6T. Currently using a Pixel 3 XL and the traditional rear (physical) sensor is so much better. I'll take Touch ID, Face ID, or modern Android rear sensors any day over these new in-screen sensors.